Compressor and turbine rotor design often requires moving air from a high (or greater) radius location to a low (or lesser) radius location. For example, a fraction of the compressor air in the main flowpath through the various stages of a compressor, is directed radially inwardly to an axially-oriented passage along the rotor. This secondary flow path supplies cooling air to the buckets in the various stages of the axially-aligned turbine section. Moving air from a higher radius to a lower radius requires the use of a rotor feature to prevent the air from free-vortexing and losing excess pressure. A common problem is that as the radius of the pumping vanes decreases, the available space for flow and the anti-swirl feature becomes limited.
The ideal impeller for radially-inflowing circuits should extend downwardly to the same radius as the axial wheel bore to which the air is being transferred. Any distance between the bottom of the impeller and the bore radius will cause the tangential velocity of the air to exceed that of the wheel. This causes higher than desired pressure losses. In addition, high-tangential velocities comprise instabilities in the flow field. Typically a flow area is limited by the axial space between the two wheels and thickness of the impellers.
There remains, therefore, a need for a compressor rotor ring configuration that provides the desired flow area that avoids excess pressure drop.